The present invention relates to wireless communications, and more particularly, to methods for determining either optimum sector widths or optimum radiation patterns within a coverage area of a wireless communication system.
The communications industry has long sought increased capacity communication systems that could bring robust communications to the world""s population. Much of today""s communication traffic is in the form of information carriers that are encoded with digital data representing information to be transported across a communication link. The information transported across the link may often include, for example, voice or video information, as well as textual information or raw data for a particular application.
With the increased use of the Internet and other forms of data communication in recent years, there has been an exponential increase in worldwide data traffic. The increased demand for data communications has essentially outpaced the capacity of existing systems, creating a need for higher capacity communication systems. The capacity of a communication link generally refers to the amount of data that can be reliably transported over the link per unit time and is typically measured in terms of data bits per second (bps).
Wireless communication systems are recognized as an economical and efficient method of interconnecting users. Wireless communication systems may be preferable, particularly in geographic locations such as congested urban areas, remote rural areas, or areas having difficult terrains, where it may be difficult and/or cost-prohibitive to deploy wire conductors or fiber optics. Rather than transporting information on data carriers over a physically xe2x80x9ctangiblexe2x80x9d communication link such as a wire conductor or fiber optic cable, wireless systems radiate data carriers in xe2x80x9copen spacexe2x80x9d throughout a coverage area. The communication link in wireless systems may be generally defined by the radiation profile of the data carriers. Many proposed wireless communication systems, however, are limited in capacity and flexibility.
Often, the data carriers radiated in wireless communication systems are frequency channels having a predetermined bandwidth and carrier frequency within a designated frequency spectrum for a given communication link. Some proposed solutions for increasing the capacity of wireless communication systems have been directed to point-to-multipoint configurations utilizing a sectored antenna system, which permits the reuse of frequency spectrum amongst multiple sectors within a coverage area. By dividing a coverage area into a number of sectors and reusing one or more frequency channels in some of the sectors, the data carrying capacity of the reused frequency channels is essentially multiplied by the number of sectors in which the channels are used.
Accordingly, frequency reuse may increase the data carrying capacity of a given xe2x80x9cslicexe2x80x9d of spectrum. However, frequency reuse as described above typically requires a sufficient degree of isolation amongst the sectors of a coverage area to insure relatively error-free data transfer. Hence, frequency reuse, and therefore increased capacity, may be achieved at the expense of increased isolation amongst the sectors. This increased sector isolation requirement may pose several engineering challenges to the design of a reliable and efficient wireless communication system.
Some proposed wireless communication systems have employed a technique of xe2x80x9cpolarization diversity,xe2x80x9d in which contiguous sectors within a coverage area use the same frequency channels, but at orthogonal polarizations. For example, in one sector, one or more frequency channels may be transmitted and received using a horizontal polarization, and in a contiguous sector, the same frequency channels would be transmitted and received using a vertical polarization, or vice versa. Other wireless communication systems have employed polarization diversity in combination with different frequency channels in contiguous sectors, while also using a number of various frequency reuse schemes in non-contiguous sectors. In general, both approaches have often met with limited success as a result of design constraints on the sectored antenna system which limit the antenna system""s performance, particularly in connection with interference amongst the sectors. As discussed above, an undesirable amount of interference amongst the sectors limits the data carrying capacity of such wireless communication systems.
In view of the foregoing, a flexible high-capacity wireless communication system which incorporates an efficient improved sectored antenna system and provides two-way broadband data services would offer several advantages to the communications industry.
The present invention is directed to methods for determining either optimum sector widths or optimum radiation patterns within a coverage area of a wireless communication system.
In various embodiments of methods according to the invention for determining an optimum sector distribution within a coverage area of a wireless communication system, the coverage area is divided into a plurality of sectors, wherein each sector has a respective sector width. The wireless communication system emits a respective radiation pattern designated for each sector.
In one embodiment, a method according to the invention comprises steps of: a) selecting the radiation pattern designated for each sector; b) selecting the sector width of each sector based on the radiation pattern; c) calculating a desired signal level in a first sector of the plurality of sectors based on the radiation pattern designated for the first sector; d) calculating a sum of undesired interference levels in the first sector based on the radiation patterns designated for at least some other sectors of the plurality of sectors except the first sector; e) calculating a ratio of the desired signal level to the sum of the undesired interference levels for the first sector; f) modifying the sector width of at least the first sector; and g) repeating steps c), d), e), and f) until the ratio for the first sector is maximized.
In another embodiment, a method according to the invention comprises steps of: a) selecting the sector width of each sector; b) selecting the radiation pattern designated for each sector based on the sector width; c) calculating a desired signal level in a first sector of the plurality of sectors based on the radiation pattern designated for the first sector; d) calculating a sum of undesired interference levels in the first sector based on the radiation patterns designated for at least some other sectors of the plurality of sectors except the first sector; e) calculating a ratio of the desired signal level to the sum of the undesired interference levels for the first sector; f) modifying the radiation pattern designated for at least one sector; and g) repeating steps c), d), e), and f), substituting the modified radiation pattern designated for the at least one sector for the radiation pattern designated for the at least one sector, until the ratio is maximized.
Other advantages, novel features, and objects of the invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.